1. Field of the Invention
The present invention generally relates to a fluid-dispensing pump for discharging a fluid stored inside a fluid-storing portion from a nozzle head disposed on the upper side of the fluid-storing portion by pressing the nozzle head.
2. Description of the Related Art
As this type of fluid-dispensing pump, for example, as described in Japanese Patent Laid-open No. 2002-066401, a fluid-dispensing pump comprising a nozzle head for discharging a fluid, a fluid-storing portion for storing the liquid, a cylinder disposed on the upper side of the fluid-storing portion, a piston which can reciprocate inside the cylinder with the nozzle head being pressed, an inflow valve mechanism for letting the fluid stored in the fluid-storing portion flow into the cylinder with an ascending motion of the piston, and an outflow valve mechanism for letting the fluid flow out to the nozzle head with an descending motion of the piston has been used.
However, because this conventional type of fluid-dispensing pumps requires high-precision work for an outer peripheral surface of the piston and for an inner peripheral surface of the cylinder so as to allow the piston to reciprocate smoothly inside the cylinder, it has a problem that fluid-dispensing pump costs become expensive.
For this reason, as described in the specification of a patent application (Japanese Patent Laid-open No. 2004-51201 or U.S. Publication No. 2004/0055457) filed by the applicant of the present invention, a fluid-dispensing pump is proposed which comprises, for example, a resinous bellows member capable of deforming from a stretched position in which it holds a relatively large amount of fluid therein to a folded-up position in which it holds a relatively small amount of fluid therein, an inflow valve mechanism coupled with the inflow opening of the bellows member, and an outflow valve mechanism coupled with the outflow opening of the bellows member. According to the fluid-dispensing pump described above, manufacturers' costs can be cut down as compared with fluid-dispensing pumps using pistons, etc.
The fluid-dispensing pump described in Japanese Patent Laid-open No. 2004-51201 or U.S. Publication No. 2004/0055457 is designed in an embodiment so that a fluid stored inside a fluid-storing portion flows into the bellows member after having passed through the inflow valve mechanism by a pressure difference occurring between inside the bellows member and outside the bellows member against the inflow valve mechanism when the bellows member deforms from a folded-up position to a stretched position. Therefore, if large load is applied to the fluid-storing portion, or if the top and bottom of the fluid-storing portion and the fluid-dispensing pump are reversed, the fluid flows into the bellows member; if inflow of the fluid into the bellows member advances, a pressure inside the bellows member against the outflow valve mechanism becomes larger than a pressure outside the bellows member by the fluid having flowed in. As a result, a problem that the fluid leaks out from the outflow valve mechanism to outside the fluid-dispensing pump occurs.
In the above, Japanese Patent Laid-open No. 2004-51201 and U.S. Publication No. 2004/0055457 describe the present inventor's own work which were published less than one year before this application, and the above descriptions apply to some embodiments disclosed therein and are in no way intended to affect their claim construction.